Improved multiple layered membrane with thin fluorine containing polymer layer

ABSTRACT

A multi-layer membrane includes a fluorine containing layer and a substrate which are joined through spray coating and heat treatment in a multi-step technique.

FIELD OF THE INVENTION

This patent applies to an improvement in the invention filed under U.S. Patent application number 20050003204, in which a thin-film fluorine containing layer of 0.3 mm or less was bonded through cross linking in a mold to substrate such as EPDM or Nitrile rubber to improve upon the substrate's physical and chemical resistance properties. The improvements in the invention are that the surface of the fluorine containing layer can be made smoother through the application of a spray-coated fluorine containing layer rather than through the previous molding method, and that the fluorine containing layer has been specifically formulated to optimize the efficiency of the product. The previous method did not offer such flexibility in formulation.

BACKGROUND OF THE INVENTION

Spray coating methods of applying fluorine containing dispersions onto substrates such as EPDM and Nitrile rubber already exist. They are typically combined with primers such as but not limited to polyamide-imide, polyether sulfones and sprayed onto a substrate that may have been pretreated with Methyl-ethyl Ketone, N-Methyl Pyrrolidone, plasma or corona treatment to improve adhesion of the primer to the substrate. Following surface preparation and priming, they are coated with a fluorine containing dispersion coating, and are then cured on-line or off-line in an oven. However such methods have not previously been applied to a diffuser membrane for use in water treatment plants, which is a difficult application.

This improvement is of particular importance in application of such a coating to a diffuser membrane used in the sewage and industrial wastewater treatment industries. Diffuser membranes are typically made from perforated non-fluorinated elastomers or polymers, which are perforated with small slits and, when inflated, produce a plume of bubbles which are released into wastewater. The efficacy of such diffusers is measured primarily in their ability to produce small bubbles in great quantity, such that the combined surface area of the bubbles is large. A large quantity of small bubbles transfers much more oxygen to the process than do a smaller quantity of large bubbles and oxygen mass transfer is desirable. Manufacturers of diffusers typically spend a great deal of time and energy formulating elastomeric compounds that produce small bubbles. The slightest compound formulation change may result in a vastly different bubble size. Furthermore, where diffuser membranes are submerged in dirty water, surface contamination from foulants such as biofilm, calcium and gypsum can cause an increase in bubble size over time, just as fats, oils, greases and solvents can penetrate traditional membranes causing chemical oxidation of the rubber. This can result in either a failed part or increased bubble size. The coating of a non fluorine containing membrane with a smooth fluorinated layer that is specifically designed to produce small bubbles, and to withstand thousands of perforations and a constant state of flux while submerged in wastewater is a novel invention and provides a universal solution to both fouling and efficiency issues. The invention described in patent application 20050003204 provides

SUMMARY OF THE INVENTION

The present invention applies to flexible diffuser membranes which are used in the aeration of wastewater and which is spray coated with a fluorine containing surface layer.

A diffuser membrane is produced from blended EPDM rubber, Nitrile rubber, or Neoprene rubber, the surface is roughened either through corona, plasma, or Methyl-ethyl Ketone, and a primer and fluorine containing surface layer are applied through spray coating. Alternately a blended primer and fluorine containing surface layer are applied through spray coating.

When treated in this way, the membrane becomes significantly more resistant to surface fouling, chemical oxidation, and its oxygen transfer efficiency is acceptably high by industry standards.

DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of a multi layered disc membrane.

FIG. 2 is a cross-sectional view of a membrane onto which layers have been applied.

FIG. 3 is a cutaway view of a multi layered tube membrane.

DETAILED DESCRIPTION

Adhesion between a spray coated fluorine containing layer and a substrate is accomplished through substrate surface treatment, priming, coating, and curing.

Firstly, a substrate layer such as membrane 3 is molded.

Secondly, a roughing agent such as corona, plasma, methyl-ethyl ketone or N-Methyl Pyrrolidone is applied to the surface to be coated as needed depending on the quality of the substrate.

Thirdly, a primer layer 2 of less than 10 microns is sprayed onto the substrate surface. This primer is then heat treated at >100 degrees C. for >15 minutes. The primer layer may contain Polyamide-Imide or Polyether Sulfone. Alternately, the primer is blended with a fluorine containing dispersion layer and this layer is sprayed onto the substrate surface, then heat treated.

Fourthly, if using separate primer and fluorine containing dispersion layers, the fluorine containing dispersion layer 1 of less than 20 microns is sprayed over the cured primer, and is heat treated at >120 degrees C. for >20 minutes. The fluorine containing dispersion layer may contain fluoride acryl resin, xylene, toluene, bentonite, titanium dioxide, carbon black, 2-Isocyanatoethyl 2,6-diisocyanatohexanoate, 2,6-Diisocyanatohexanoic acid 2-isocyanatoethyl ester and/or ethyl acetate.

From the foregoing it will be seen that this invention is one well adapted to attain all ends and objectives hereinabove set forth together with the other advantages which are obvious and which are inherent to the structure.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

Since many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative, and not in a limiting sense. 

1. A multi-layer membrane comprising; a first layer comprising a polymer layer on a membrane; and a second layer over said first layer comprising a dispersion layer wherein said dispersion layer is a fluorine containing dispersion layer.
 2. The multi-layer membrane of claim 1, wherein said first layer comprises a fluoroelastomer.
 3. The multi-layer membrane of claim 1, wherein said dispersion layer further includes a primer and a fluorine containing dispersion.
 4. The multi-layer membrane of claim 1, wherein said first layer further includes material selected from a group consisting of neoprene rubber, ethylene propylene diene monomer (EPDM) and nitrile rubber.
 5. The multi-layer membrane of claim 1, wherein said first layer further includes a primer layer and wherein said primer layer is less than 10 microns.
 6. The multi-layer membrane of claim 1, wherein said membrane is selected from a group consisting of a tubular shaped membrane, a disc shaped membrane and a panel shaped membrane.
 7. The multi-layer membrane of claim 5, wherein said primer layer comprises material selected from a group consisting of Polyamide-Imide and Polyether Sulfone.
 8. The multi-layer membrane of claim 1, wherein said second layer is less than 20 microns.
 9. The multi-layer membrane of claim 1, wherein said second layer is less than 20 microns and said second layer is heat treated at a temperature of greater than 120 degrees C.
 10. The multi-layer membrane of claim 1, wherein said second layer further comprises material selected from a group consisting of fluoride acryl resin, xylene, toluene, bentonite, titanium dioxide, carbon black, 2-Isocyanatoethyl 2,6-diisocyanatohexanoate, 2,6-Diisocyanatohexanoic acid 2-isocyanatoethyl ester and ethyl acetate.
 11. The multi-layer membrane of claim 1, wherein said first layer is a non-fluorinated polymer.
 12. The multi-layer membrane of claim 1, wherein a primer and said fluorine containing dispersion are is applied onto said first layer in a single application.
 13. The multi-layer membrane of claim 1, wherein said second layer is applied through a spray, and is cured using a method selected from a group consisting of an in-line oven and an off-line oven.
 14. The multi-layer membrane of claim 1, wherein said first layer further includes materials selected from a group consisting of fluoride acryl resin, methyl-ethly ketone, xylene, toluene and carbon black.
 15. The multi-layer membrane of claim 1, wherein said membrane is pretreated with plasma, corona, N-Methyl Pyrrolidone or methyl-ethyl ketone prior to coating of said first layer.
 16. A process for preparing a multi layer membrane wherein said membrane comprises of a polymer layer consisting of a fluorine containing polymer, a substrate, wherein a bond between said first layer and said second layer is formed first via a degreasing step. followed by primer, heat treatment of said primer, spray coating of a fluorine containing dispersion, and finally heat treatment of said coating.
 17. A process for preparing a multi layer membrane wherein said membrane comprises of a polymer layer consisting of a fluorine containing polymer, a substrate, wherein a bond between said first layer and said second layer is formed first via a degreasing step. followed by a spray coating of combined primer and fluorine containing dispersion, and finally heat treatment of said combined primer and said coating.
 18. A process for preparing a multi layer membrane wherein said membrane comprises of a polymer layer consisting of a fluorine containing polymer, a substrate, wherein a bond between said first layer and said second layer is formed via a spray coating of combined primer and fluorine containing dispersion, and finally heat treatment of said combined primer and said coating.
 19. A process for preparing a multi layer membrane wherein said membrane comprises of a polymer layer consisting of a fluorine containing polymer, a substrate, wherein a bond between said first layer and said second layer is formed via a spray coating of a primer, heat treatment of said primer, spray coating of fluorine containing dispersion, and finally heat treatment of said coating.
 20. The multi-layer membrane of claim 1, wherein said membrane is pretreated prior to coating of said first layer. 